While training for the upcoming U.S. leg of U2's 360 degrees tour, the singer experienced severe back pain and partial paralysis of his leg before he was admitted to Maximilians-University Hospital in Munich, according to a statement on his website.

"Surgery was the only course of treatment for full recovery and to avoid further paralysis," said Dr. Jorg Tonn, who performed the operation, in a press release. Tonn said Bono's prognosis was excellent.

"Maybe he just overdid it and hurt himself," bandmate the Edge said in a Skype interview posted to U2's website.

With months of recovery ahead of him, Bono had to call off -- at least for now -- U2's North American tour.

In an interview posted to U2's website, Bono said he was "heartbroken" about the cancellation. U2's manager, Paul McGuinness said, "'Our biggest, and I believe best tour, has been interrupted, and we're all devastated ... but the most important thing right now is that Bono make a full recovery."

Bono was released from the Munich hospital Tuesday and will follow a rehab regimen for at least eight weeks.

How Did Bono Bust His Back?

With a herniated disc, the gelatinous disc that cushions the vertebra tears, explained Dr. Andrew Hecht, assistant professor of neurosurgery at Mount Sinai Medical Center in New York. Pieces of the disc can then "go into the spinal canal where the nerves live and cause pain, numbness or tingling, weakness or all three," he said.

Doctors found an 8 millimeter tear in Bono's disc.

Herniated disc surgeries are one of the more common procedures neurosurgeons do, said Dr. Michael Lim, a neurosurgeon at John's Hopkins University. Usually, they just "find the nerve root that is compressed and work around it to remove the herniated fragment," he said.

Even for pro athletes with the same injury, "90 percent go back to the same elite level of sport after the operation," Hecht said. Although Bono is not his patient, Hecht said Bono would likely "go back to full function and quality of life," but he might need more than eight weeks of rehab.

"If you're a musician and you're going to be dancing around the stage, that's a very athletic endeavor and usually takes 12 to 14 weeks to recover" to this level of activity, Hecht said.

Too Old to Rock?

Overdoing it in a stage performance might have caused the U2 singer's injury in the first place.

There can be one particular event triggering the injury, Hecht said, or it can be "just a gradual wearing out of the lining [of the disc], and one day it just pops open."

"As you get older, there's a higher risk of a herniated disc, but it's often not related to age as much as is it to stress on the spine," said Lim.

McGuinness, U2's manager, said in a statement that Bono was injured during training for the tour, and the Edge suggested in a Skype interview that Bono may have been overdoing it:

In his excitement for the tour, Bono "is not somebody who … considers physical limitations. He's just about moving forward at full speed."

But now that Bono is in his sixth decade, perhaps he should learn from the experience of the other 50-plus rock 'n' rollers.

Last summer, 62-year-old Steven Tyler of Aerosmith took a tumble on the stage while touring, and broke his shoulder and injured his head and neck. The band had to call off the rest of the 2009 tour.

In some ways, noted the Edge in the interview, it may be a blessing in disguise that this injury came up before the tour began

"Knowing him, he'll want to take some shortcuts and get ahead of himself, [but] we'll be there to chain him down if need be," he said.

"He needs to listen to his body," said Hecht, and allow full recuperation because the biggest complication from this surgery is reherniating the same disc by going back to activity too soon, which occurs 5 to 8t percent of the time.

With care and proper recovery, "the vast majority of these cases go back to [their] life and usual activities," Hecht said, "including being a rock star."